全文获取类型
收费全文 | 523篇 |
免费 | 25篇 |
国内免费 | 1篇 |
专业分类
化学 | 416篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 36篇 |
物理学 | 85篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 13篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 21篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 22篇 |
2009年 | 14篇 |
2008年 | 30篇 |
2007年 | 26篇 |
2006年 | 39篇 |
2005年 | 41篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 27篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有549条查询结果,搜索用时 51 毫秒
41.
Dr. Louwanda Lakiss Dr. Aurélie Vicente Prof. Jean-Pierre Gilson Dr. Valentin Valtchev Dr. Svetlana Mintova Dr. Alexandre Vimont Dr. Robert Bedard Dr. Suheil Abdo Dr. Jeffery Bricker 《Chemphyschem》2020,21(16):1873-1881
We outline two methodologies to selectively characterize the Brønsted acidity of the external surface of FAU-type zeolites by IR and NMR spectroscopy of adsorbed basic probe molecules. The challenge and goal are to develop reliable and quantitative IR and NMR methodologies to investigate the accessibility of acidic sites in the large pore FAU-type zeolite Y and its mesoporous derivatives often referred to as ultra-stable Y (USY). The accessibility of their Brønsted acid sites to probe molecules (n-alkylamines, n-alkylpyridines, n-alkylphosphine- and phenylphosphine-oxides) of different molecular sizes is quantitatively monitored either by IR or 31P NMR spectroscopy. It is now possible, for the first time to quantitatively discriminate between the Brønsted acidity located in the microporosity and on the external surface of large pore zeolites. For instance, the number of external acid sites on a Y (LZY-64) zeolite represents 2 % of its total acid sites while that of a USY (CBV760) represents 4 % while the latter has a much lower framework Si/Al ratio. 相似文献
42.
Jenna M. Allan Md Abdul Mumin Jeffery A. Wood William Z. Xu Wei Wu Paul A. Charpentier 《Journal of Polymer Science.Polymer Physics》2014,52(14):927-935
Poly(ethylene‐co‐vinyl acetate) (EVA) plastic films are widely used for solar coverings including photovoltaic modules and commercial greenhouse films, but are poor at controlling heat flow. In this work, silica aerogel (SA) nanogels were examined for preparing transparent heat retention EVA films that block far infrared spectra radiation to maintain heat, without compromising the optical performance of the films. SA nanogels were melt‐mixed using a mini twin‐screw extruder with EVA pellets to form SA/EVA composite, which were pressed into thin films with controlled thickness. The composite films were characterized in terms of optical properties using a variety of analytical methods including FTIR, UV–Vis spectroscopy, electron, confocal, and atomic force microscopy. Both thermicity and thermal conductivity of commercial and experimental SA/EVA films were measured. The results demonstrated that the SA/EVA films gave improved infrared retention compared to commercial thermal plastic films without compromising visible light transmission, showing the potential for this approach in next generation heat retention films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 927–935 相似文献
43.
Dr. Todd R. Zeitler Timothy Van Heest Prof. David S. Sholl Dr. Mark D. Allendorf Dr. Jeffery A. Greathouse 《Chemphyschem》2013,14(16):3740-3750
A set of 98 nanoporous framework material (NFM) structures was investigated by classical Grand canonical Monte Carlo simulations for low-pressure O2 adsorption properties (Henry’s constant and isosteric heat of adsorption). The set of materials includes those that have shown high O2 uptake experimentally as well as a subset of more than 2000 structures previously screened for noble-gas uptake. While use of the general force field UFF is fruitful for noble-gas adsorption studies, its use is shown to be limited for the case of O2 adsorption—one distinct limitation is a lack of sufficient O2–metal interactions to be able to describe O2 interaction with open metal sites. Nonetheless, those structures without open metal sites that have very small pores (<2.5 Å) show increased O2/N2 selectivity. Additionally, O2/N2 mixture simulations show that in some cases, H2O or N2 can hinder O2 uptake for NFMs with small pores due to competitive adsorption. 相似文献
44.
45.
Jeffery L. Tollefson 《Topology》1981,20(4):323-352
46.
[reaction: see text] A novel approach to the formation of the unusual pyrone-containing ring systems as found in polypropionate metabolites from the Tridachia family of marine molluscs has been developed. This approach includes an intramolecular cyclization of a beta-keto acid onto a cyclohexenone ring to afford a fused, bicyclic pyrone. 相似文献
47.
[reaction: see text] The solid-phase assembly of heterocyclic amino acids enabled the total synthesis of numerous diastereoisomers of tenuecyclamides A-D, establishing or correcting the stereochemistry of each natural product. This strategy provides a very efficient route to synthesize thiazole- and oxazole-containing macrolactams from heterocyclic amino acids that are readily prepared from Fmoc-alpha-amino acids. This methodology appears to be broadly applicable to the synthesis of natural product libraries incorporating unnatural heterocyclic amino acid residues for the purpose of drug discovery. 相似文献
48.
Harding LP Jeffery JC Riis-Johannessen T Rice CR Zeng Z 《Dalton transactions (Cambridge, England : 2003)》2004,(16):2396-2397
The amide-substituted unsymmetrical ligand L(1) upon coordination to Co(2+) forms the dinuclear triple helicate [Co(2)(L(1))(3)](4+) which exists as both possible C(1) and C(3) symmetric geometric isomers in solution, however, upon addition of nitrate ions, the formation of an anion binding cavity is favoured and hence the sole product is the C(3) symmetric isomer in which all three amide substituents are hydrogen bonded to the nitrate anion. 相似文献
49.
50.